The present invention generally relates to power units having multiple power sources and more particularly to an apparatus and method for coupling the output members of multiple power sources.
Engines in current production automobiles are typically sized to meet certain performance requirements. For normal city and highway driving, the engine is operated at low loads, which means low engine efficiency and high fuel consumption as a result. Several approaches have been proposed to modify the powertrain of a vehicle such that it results in higher engine efficiency. One solution that has been proposed to address this problem is disclosed in commonly assigned U.S. patent application Ser. No. 09/466,148, the disclosure of which is hereby incorporated by reference as if fully set forth herein. This patent application discloses a hybrid vehicle having a dual engine power unit. When the vehicle is operated at a relatively modest rate, only one of the engines is employed to propel the vehicle. When the power demanded from the power unit exceeds the single engine output, the second engine is employed to supplement the power output from the power unit. Several problems have been noted with this arrangement, however.
Primarily, these problems relate to the coupling of the output members of the engines. The coupling mechanism and method should be highly reliable and provide smooth coupling that is transparent to the vehicle operator, yet be relatively inexpensive. Furthermore, the coupling mechanism and method should permit the engines to be coupled relatively quickly, so as to minimize or eliminate altogether, the lag time between the vehicle operator""s demand for additional power and the delivery of additional power via the second engine.
In one preferred form, the present invention provides a method for coupling a first rotational output member to a second rotational output member. The method includes the steps of accelerating the second rotational output member at a first predetermined rate of acceleration until a rotational speed of the second rotational output member is less than a rotational speed of the first rotational output member by a first predetermined threshold; accelerating the second rotational output member at a second predetermined rate of acceleration until the rotational speed of the second rotational output member is equal to the rotational speed of the first rotational output member, the second predetermined rate of acceleration being less than the first predetermined rate of acceleration and the second predetermined threshold being less than the first predetermined threshold; and coupling the first and second rotational output members.
In another form, the present invention provides a power unit having a first power source with a first rotational output member, a second power source with a second rotational output member, a one-way clutch, a power input mechanism and a controller. The one-way clutch has a clutch input that is rotatably coupled to the second rotational output member and a clutch output. The one-way clutch is normally disengaged and does not permit torque transmission between the clutch input and the clutch output. It permits torque transmission when it is in the locked position. It is said to be in the locked position when the speed of the clutch input is the same as that of the clutch output. The power input mechanism includes a first input, which is coupled for rotation with the first rotational output member, a second input, which is coupled for rotation with the clutch output, and a transmission output, which is rotatably coupled to the transmission input member. The controller controls the first and second power sources and determines when a power demand on the transmission output exceeds a predetermined power demand threshold. In response to the determination that the power demand on the transmission output exceeds a predetermined power demand threshold, the controller controls the second power source to accelerate the second rotational output member at a first predetermined rate of acceleration until a rotational speed of the second rotational output member is less than a rotational speed of the first rotational output member by a first predetermined threshold, and thereafter accelerate the second rotational output member at a second predetermined rate of acceleration until the rotational speed of the second rotational output member is equal to the rotational speed of the first rotational output member, the second predetermined rate of acceleration being less than the first predetermined rate of acceleration and the second predetermined threshold being less than the first predetermined threshold.
In yet another preferred form, the present invention provides a method for coupling a first rotational output member to a second rotational output member. The method includes the steps of operating a first power source such that all of the torque input to a power input mechanism is supplied by the first power source; operating a second power source such that a rotational speed of the second rotational output member is matched to a rotational speed of the first rotational output member; coupling the first and second rotational output members; and simultaneously controlling the first and second power sources such that the rotational speeds of first and second rotational output members remain matched and a ratio of power supplied to the power input mechanism by the second and first power sources increases from 0:1 to a predetermined ratio.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.